The mission of this Program is to prepare a cadre of outstanding cancer epidemiologists through rigorous academic training in research methodology and the epidemiology and biology of cancer, and/or mentored research. Those in the Molecular & Genetic Epidemiology Sub-program receive additional training in the application of molecular genetic techniques to epidemiologic research. A distinguished faculty provides substantial opportunity for research experience. There are three types of trainees: Doctoral Candidates in Epidemiology include both pre-doctoral candidates and those holding a prior doctoral degree (generally clinicians) who undertake 2-3 years of coursework in addition to research; Clinical Researchers include physicians with specialty training in cancer preparing for careers in clinical epidemiology who undertake a one year Master's degree program in methodology followed by a year of research; and Post-doctoral Fellows who hold a prior doctora! degree in Epidemiology or in Biology and undertake mentored research (and coursework if needed) in preparation for an academic career. Trainee positions are generally awarded for 2 or 3 years. The number of trainees requested include 3-4 pre-doctoral and 1-2 post-doctoral Doctoral Candidates; 2 Clinical Researchers; 2 Post-doctoral Fellows with an additional 4 pre-doctoral Doctoral Candidates and 3 Post-doctoral Fellows in the Sub-program for a total of 16 trainees. The Program is based in the Department of Epidemiology of the Harvard School of Public Health. A dedicated molecular epidemiology laboratory is available. This proposal continues a long history of excellence in training in cancer epidemiology at Harvard University.